The composite pipe in question finds use within different fields of industry where fluids need transporting, and is characterized through low weight, high strength and high chemical resistance. Advantageously, though not exclusively, the composite pipes may be employed as flexible risers, flow-lines, pipe-lines, umbilical pipes, pressure casings for process equipment, containers and structural members within the oil and gas industry.
Composite pipes of the type referred to are known to be produced by winding and consolidating a strip- or band-shaped, fibre reinforced thermoplastic, known as a prepreg, about a tubular base that conventionally remains inside the consolidated thermoplastic, thus forming an internal liner which is bonded to the external pipe wall made of cured thermoplastic material. The term “prepreg” refers to a mat, fabric, non-woven material or roving pre-impregnated with resin. The fibre reinforced thermoplastic recited above is a polymer composite which is partially cured and ready for moulding, comprising fibres embedded in a matrix of thermoplastic polymer material which solidifies into the shape applied when cooled from a temperature effective for melting of the matrix. The solidifying process is called consolidation. The fibres may extend in essentially the one and same direction in a unidirectional manner.
Among the prior art available, reference can be made to WO2005/108046 A1, as well as WO2003/037770A1, each of which represents the prior art which includes the composites pipes having internal liners.
Likewise, JP-1198343 discloses a method by which a layer of prepreg material is wound onto a base layer comprising a carbon paper which is previously wound about a mandrel. The paper base and prepreg layers are baked together, whereupon the mandrel is pulled out from the resulting baked body. Pipes of specified lengths adapted to the length of the mandrel are produced this way, and released by pulling the mandrel out from the resulting pipe.
Composite pipes having an internal liner bonded to external structural layers made of thermoplastic materials may suffer the occurrence of cracks and separation between the internal liner and the exterior thermoplastic layer. One plausible cause for such separation and cracks formation is the use of different materials having different material properties for structuring the liner and thermoplastic external layer, respectively. The conditions under which the composite pipe operates may contain temperature differentials over the pipe wall in the order of several hundred degrees C., pipes combined in lengths that cover kilometer distances, transversal movements and bending causing contra-directional axial loads on the pipe layers, high pressures prevailing at substantial sea depths, etc.
An object of the present invention is thus to reduce or essentially eliminate the drawbacks related to the pipes structured through the combination of an internal liner which is bonded to an external pipe wall.
Another object is to provide a method and assembly through which homogenous composite pipes of unspecified lengths, or endless pipes, are producible.
These objects are met in a composite pipe as produced through the method.
The objects are likewise met in a composite pipe as produced through the assembly for carrying out the method.
Briefly, in the present invention there is provided a production method and an assembly by which multiple layers of fibre reinforced thermoplastic strips are applied onto a mandrel to fabricate a homogenous composite pipe of unspecified length.
The method of the present invention comprises the steps of: arranging a mandrel stationary in a process direction to extend freely from a first supported end to a second end; applying a slip-sheath about the mandrel; winding the thermoplastic material strips about the slip-sheath; and consolidation of a section of the thermoplastic material strip winding. The method is further characterized through the steps of forming the slip-sheath from tape material which is applied longitudinally onto the mandrel surface; connecting the slip-sheath to a pulling means arranged downstream of the mandrel in the process direction, and pulling consolidated pipe sections off from the second end of the mandrel in synchronization with the steps of winding and consolidation.
The steps of winding and consolidation may be synchronized with an incremental pulling of consolidated sections of composite from the mandrel, or may alternatively be synchronized with a continuous pulling of consolidated sections of composite from the mandrel.
Preferably, the slip-sheath material is a liquid-soluble material tape, and most preferred a cellulose fibre in a matrix of water-based resin formed into a tape, which is applied about the mandrel in advance of the winding of strips of fibre reinforced thermoplastic, as seen in the process direction.
Advantageously, the winding is performed from singular or multiple supplies of fibre reinforced thermoplastic driven through a revolving path about the mandrel.
The revolving supplies of fibre reinforced thermoplastic may be arranged for a reciprocating motion in the process direction, or may alternatively and preferred be stationary arranged, with respect to the process direction.
Consolidation of the fibre reinforced thermoplastic is performed through the supply of heat to the wound strips of fibre reinforced thermoplastic at a location upstream of the second end of the mandrel. A heater with a capacity to apply, circumferentially, a temperature necessary for melting the polymer matrix of the fibre reinforced thermoplastic, may be arranged for reciprocating motion in the process direction, though alternatively and preferred the heater is stationary with respect to the process direction.
Pulling the homogenous composite pipe off from the second end of the mandrel comprises further winding of consolidated pipe sections onto a large diameter spool.
In the method, a finishing step comprises cleaning the pipe interior from residues of slip-sheath material. The cleaning step may involve flooding the pipe interior with water, and/or mechanically removing residues of slip-sheath material from the pipe interior.
An assembly by which a homogenous composite pipe of unspecified length is produced according to the method briefly comprises a mandrel which is stationary supported in a first end to extend freely in a process direction from said first end to a second end; means for forming a slip-sheath about the mandrel; a winder mechanism revolving about the mandrel downstream of said first end carrying at least one supply of thermoplastic material strips; and a heater surrounding the mandrel upstream of said second end. The assembly is further characterized in that said means for forming the slip-sheath about the mandrel is arranged to apply a tape material longitudinally onto the mandrel surface, and in that a pulling means is arranged downstream of the mandrel to be connectable to the slip-sheath.
The operations of the winder mechanism and heater are synchronized with an incremental operation of the pulling means. Alternatively and preferred, the operations of the winder mechanism and heater are synchronized with a continuous operation of the pulling means.
In a preferred embodiment, the slip-sheath applying means comprises at least one rotary supply of tape-shaped slip-sheath material arranged upstream of the winding mechanism for feeding the tape longitudinally along the mandrel. The slip-sheath applying means advantageously comprises a tape guide funnel arranged for forming the tape circumferentially about the mandrel.
Advantageously, the pulling means comprises a large diameter spool driven for rotation, onto which the composite pipe sections is wound from the mandrel.
Advantageously, the method and assembly of the present invention are implemented in the production of a homogenous composite pipe suitable as a flow-line for transportation of fluids, such as oil and/or gas.
The method and assembly of the present invention are likewise advantageously implemented in the production of a homogenous composite pipe suitable as a sub-sea structure for the off-shore industry.
The method and assembly of the present invention are also advantageously implemented in the production of a homogenous composite pipe suitable as a production or injection riser for oil and/or gas and/or water.
The method and assembly of the present invention are likewise advantageously implemented in the production of a homogenous composite pipe suitable as an umbilical pipe.
The invention thus makes fabrication of unspecified or continuous lengths of homogenous composite pipes possible, without relying on a tubular member remaining inside the finished pipe as an internal liner.
The present invention provides an advantage above the prior art in that homogenous pipe sections of unspecified length are producible in a continuous manner, in other words endless pipes may be produced. In contrast to a helically applied base layer, such as the one disclosed in JP-1198343, a slip-sheath applied in longitudinal direction onto the mandrel surface as disclosed in the present invention provides reduced frictional resistance as consolidated pipe sections are successively pulled off from the stationary mandrel. By building the slip-sheath from tapes extending in longitudinal direction, and connecting a pulling means to the slip-sheath, the pulling force applied is fully absorbed by the slip-sheath and the helical windings of thermoplastic strips remain unaffected from any tensile stresses that would otherwise be applied from the pulling means. This aspect is considered to be of importance in the continuous production of pipes of unspecified lengths, wherein unconsolidated sections of helically wound thermoplastic strips are moving along the mandrel as consolidated sections of the pipe are pulled off from the mandrel.
The present invention is more closely explained below, with reference made to the accompanying drawing.